Communication devices such as wireless devices may be also known as e.g. user equipments (UEs), mobile terminals, wireless terminals and/or mobile stations. A wireless device is enabled to communicate wirelessly in a cellular communications network, wireless communications system, or radio communications system, sometimes also referred to as a cellular radio system or cellular network. The communication may be performed e.g. between two wireless devices, between a wireless device and a regular telephone and/or between a wireless device and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the cellular communications network.
The wireless device may further be referred to as a mobile telephone, cellular telephone, laptop, Personal Digital Assistant (PDA), tablet computer, surf plate, just to mention some further examples. The wireless device in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile device, enabled to communicate voice and/or data, via the RAN, with another entity, such as another wireless device or a server.
The cellular communications network covers a geographical area which is divided into cell areas, wherein each cell area is served by at least one base station, e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. “eNB”, “eNodeB”, “NodeB”, “B node”, or BTS (Base Transceiver Station), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. Cells may overlap so that several cells cover the same geographical area. By the base station serving a cell is meant that the radio coverage is provided such that one or more wireless devices located in the geographical area where the radio coverage is provided may be served by the base station. One base station may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the wireless device within range of the base stations.
In some RANs, several base stations may be connected, e.g. by landlines or microwave, to a radio network controller, e.g. a Radio Network Controller (RNC) in Universal Mobile Telecommunications System (UMTS), and/or to each other. The radio network controller, also sometimes termed a Base Station Controller (BSC) e.g. in GSM, may supervise and coordinate various activities of the plural base stations connected thereto. GSM is an abbreviation for Global System for Mobile Communications (originally: Groupe Spécial Mobile). In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or eNBs, may be directly connected to other base stations and may be directly connected to one or more core networks.
UMTS is a third generation mobile communication system, which evolved from the GSM, and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UMTS Terrestrial Radio Access Network (UTRAN) is essentially a radio access network using wideband code division multiple access for wireless devices. High Speed Packet Access (HSPA) is an amalgamation of two mobile telephony protocols, High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA), defined by 3GPP, that extends and improves the performance of existing 3rd generation mobile telecommunication networks utilizing the WCDMA. Moreover, the 3GPP has undertaken to evolve further the UTRAN and GSM based radio access network technologies, for example into evolved UTRAN (E-UTRAN) used in LTE.
In the context of this disclosure, the expression downlink (DL) is used for the transmission path from the base station to the wireless device. The expression uplink (UL) is used for the transmission path in the opposite direction i.e. from the wireless device to the base station.
Long Term Evolution-Advanced (LTE-A) is e.g. specified as part of a Release 10 of 3GPP specifications and it offers higher data rates than previous releases. One way of accomplishing this is through so called Carrier Aggregation (CA) where more than one carrier is used to thereby increase the overall transmission bandwidth. LTE-A defines three carrier-aggregation scenarios: single-band (or intra-band) contiguous, single-band non-contiguous, and multiband (inter-band) non-contiguous. Carrier aggregation is supported by both Frequency Division Duplex (FDD) and Time Division Duplex (TDD) in LTE. Each carrier involved in CA is referred to as a Component Carrier (CC) and belong to either one of two categories: Primary Component Carrier (PCC) and Secondary Component Carrier (SCC). There is one downlink PCC (DL PCC) and one associated uplink PCC (UL PCC), and may be one or more SCCs, including both UL SCCs and DL SCCs. When carrier aggregation is used there are a number of serving cells for each UE being served, one serving cell for each CC, i.e. one primary serving cell and one or more secondary serving cells. The coverage of the serving cells may differ. Connection of a UE in LTE through Radio Resource Control (RRC) is handled by the primary serving cell that thus is served by the PCC, or more specifically the DL and UL PCC. It is also on the DL PCC that the UE receives Non-Access Stratum (NAS) information, such as security parameters and in idle mode the UE listens to system information on the DL PCC. Physical Uplink Control CHannel (PUCCH) is sent on the UL PCC. The SCCs may be added and removed as required, while the PCC is only changed at handover. The eNB decides which cell that is the primary serving cell, which is taken care of by handover, and it can also decide that a UE shall utilize one or more SCCs, i.e. be served in one or more secondary serving cells. The configuration of, and activation and deactivation of, CCs may, for example, be based on measurements performed by eNBs and/or UEs. The decision to configure and serve a UE using CA may also be based on the type services, and thus radio bearers, that the UE is or may be associated with and the capabilities of the UE.
It is realized that a wireless communications system applying CA require, or at least may benefit, from various aspects of adaptation compared to a conventional situation without CA since there are multiple serving cells involved at the same time, not only one as conventionally is the case. It is further desirable that any adaptation is backwards compatible so that wireless devices that do not support CA may coexist with wireless devices that do support CA.